Abstract

Mortality in Pinus sp. in Sardinia - in particular, P. radiata D. Don -
was investigated between 1976 and 1978. Preliminary studies had revealed
an association between Macrophomina phaseolina (Tassi) Goid. (the causal
agent of charcoal root rot disease) with affected plants.
The disease occurred on plants of different ages in 24 of the main P.
radiata plantantions and nurseries. In every case, the presence of M. pllaseolina
was confirmed. The disease varied in spread and severity from
rather low to very high values. It was also recorded on P. pinea L., P.
halepensis Mill., P. patula Schl. et Cham., P. pinaster Sol. and P. nigra
Arn. ssp. Laricio (Poir.) Palabin Coste.
The occurrence of infection, the symptomatological progress of thc disease and microscopic characteristics of affected tissues wcrc invcstigntcd
both in the field and in the laboratory. Data concerning the incidence of
disease - which first became serious in 1975, showed a low value in 1976 and
1977 and increased again in 1978 - were obtained by field obscrvation
and trials in experimental plots.
Several strains of Macrophomina phaseolina were isolated from affectcd
plants. They were very similar morphologically and in their tempe·
rature responses. Regarding microsc1erotia size, thcsc strains can bc included
in Haigh's «C-type ».
Environmental factors favouring the development of the disease were
investigated. Analysis revealed that the occurrence of disease in the field
can be attributed both to affected plants having come from nurseries and to
direct infection due to presence of Cistus monspeliensis in the planting arca.
Seeds of other Pinus species were disease-free. Some planting systems
appear to favour the development of the disease in certain climatic conditions.
In particular, a combination of high temperature and prolonged
periods of water stress increase infection with M. phaseolina.